The present invention relates to a sustained release dispenser of sex pheromone of insects or, more particularly, to a dispenser capable of sustainedly releasing a sex pheromone of an insectan pest at a constant or controlled rate over a long period of time to control the population of the insect species.
It has been an important technical problem to develop a method for sustainedly releasing a sex pheromone compound of an insectan pest of a particular species at a constant rate over a long period of time into the field. For example, it is already practiced to prepare a dispenser form containing a sex pheromone compound from which the sex pheromone compound is vaporized and emitted at a controlled rate. It would be a desirable ideal if the rate of the pheromone emission could be maintained at a level to exhibit the desired effect over a necessary length of time under meteorologically different conditions such as temperature, humidity, wind velocity and the like. When dispenser bodies having barrier walls made of the same polymeric material are used for enclosing different sex pheromone compounds, however, no satisfactory results can be obtained in respect of the rate of emission for all kinds of the pheromone compounds since the rate of pheromone emission may be too large for one sex pheromone compound while the rate may be too small for the other.
When the rate of pheromone emission from a dispenser is too large, the serviceable life of the dispenser form is naturally unduly short. When the rate of emission is too small, an economical disadvantage may be caused because a considerable portion of the sex pheromone compound initially contained in the dispenser form may be left unutilized therein still after expiration of the necessary length of time.
An unduly short serviceable life of a dispenser form may cause an uneconomically large consumption of man power since distribution of the dispenser forms over the field must be repeated several times during a season in which the effect of the sex pheromone compound should be continuedly exhibited. Moreover, a serious problem may be sometimes caused that the desired effect of the pheromone compound can no longer be exhibited entirely at the latest stage of the serviceable life of the dispenser form due to exhaustion of the pheromone compound contained in the dispenser form.
It is of course that the number of the dispenser forms of a sex pheromone compound to be distributed over a unit area of the field should desirably be as small as possible provided that the effect of the pheromone compound is not affected so much. Unfortunately, no dispenser form has yet been developed which can maintain the necessary rate of pheromone emission over the season even by a single time of distribution of a relatively small number of the dispenser forms in the field.
The inventors have previously developed a dispenser form for sustainedly releasing a sex pheromone compound of insects prepared by filling a polyethylene-made tube having an inner diameter of 0.8 mm, outer diameter of 1.45 mm and length of 200 mm with the sex pheromone compound and performed a field test by using a number of such dispensers (U.S. Pat. No. 4,600,146). In the field test undertaken in the State of Arizona, U.S.A., with an object to control the population of pink bollworms, 894 dispensers, each filled with 72 mg of Z,Z/E-7,11-hexadecadienyl acetate as the sex pheromone of the insects, were distributed per hectare of the field. In this case, the rate of pheromone emission was constantly maintained at about 0.6 mg/day for each dispenser over a period of about 30 days to exhibit sufficiently high effects of intercommunication disruption between different sexes of the insects. Unfortunately, the rate of pheromone emission was decreased to 0.4 mg/day or below for each dispenser after lapse of 50 days so that the desired effect of intercommunication disruption could no longer be fully exhibited [Journal of Economic Entomology, volume 78, No. 6, pages 1431-1436 (1985)].